The present invention relates to a light barrier arrangement for automatically actuated lift cabin doors.
Generally speaking, such an arrangement includes at least one light receiver and at least one light emitter or transmitter connected with the lift cabin door and arranged to be displaced together with the same and with light beams or rays extending approximately vertically upwardly from the door sill. Any interruption in the light beam or radiation will generate a signal acting on the lift cabin door drive. In particular, the present invention also relates to a light barrier arrangement of the aforementioned type in combination with a lift or elevator cabin door which comprises two cabin doors defining a central closing line.
In a known light barrier arrangement as disclosed in German Pat. No. 1,007,036 a beam of light is caused to extend vertically along the closing line of an elevator or lift cabin having twin doors. The light emitter or transmitter is mounted above the door opening and the light receiver is mounted below the door sill. The protection offered by this type of light barrier is insufficient, since any persons passing laterally of the light beam will not be detected during the door closing movement. Also, in an arrangement of this type it is possible that the door control is interrupted unnecessarily and prematurely, so that there results a loss of time.
In a prior art light barrier arrangement as disclosed in U.S. Pat. No. 3,063,516 which contains a horizontally extending beam of light, the light emitter is mounted at one half of the cabin door and the light receiver at the other half of the cabin door. The cabin door halves comprise movable edges generating an additional protection which, when contacted, may interrupt the beam of light. Also in this case protection during closing movement of the cabin door is insufficient, and a premature and unnecessary interruption in the door control is possible due to the use of only one horizontally extending beam of light.
Part of the disadvantages mentioned above are avoided according to another known monitoring device for automatically closing lift cabin doors as disclosed in German Patent Publication No. 2,459,674. In this case, the door sill has a number of apertures distributed over the entire width of the door opening. Lenses are inserted into the apertures and light emitted from a light source passes through the lenses. Two light sensors or receivers of a light barrier arrangement which is independent of the door position are secured at the upper edge of the door opening at a distance of roughly 30 centimeters and symmetrically with respect to the door closing line. Two further light sensors or receivers associated with a light barrier responsive to the door position are also mounted at the upper edges of the doors. The last-mentioned light sensors or receivers are intended to respond to obstacles close to the door edge, for example, in a region up to 75 mm. It is a disadvantage of the light barrier arrangement which is independent of the door position that the door control may be prematurely interrupted. A further disadvantage is the relatively expensive manufacturing process for the door sill including the light exit apertures distributed over the entire width of the door which additionally are prone to being covered by dirt.
To avoid an unnecessary and premature interruption in the door control and also to thus save time, it is desirable to limit the detection of obstacles to a region adjacent to the closing edges of the door. Therefore, it has been contemplated for the light barrier arrangement depending on the door position in the monitoring device discussed heretofore with respect to German Patent Publication No. 2,456,674 to mount light emitters or transmitters at the lower edges of the doors. The light, then, will be incident at the door sill and by reflection therefrom reaches the light receivers. What is here a disadvantage is that the surface of the door sill must be suited for scattered reflections. This requires either specific materials or a specific surface finishing. In case of smoothing due to use, contamination or outside light, there may arise conditions under which the operation of such light barrier arrangement is no longer faultless.